View Compilation Error

0_0_37557330_17766.cpp:5:7: error: expected nested-name-specifier before 'namespacestd'
 using namespacestd;
       ^
0_0_37557330_17766.cpp: In function 'int main()':
0_0_37557330_17766.cpp:50:5: error: 'return0' was not declared in this scope
     return0;
     ^